Despite their significant and growing importance, with implications across a range of policy areas, information on Multinational Enterprises (MNEs) remains at best patchy. This is partly a function of complexity: by their very nature, MNEs are large, with a multitude of activities across a number of jurisdictions. However, for firms engaging in fiscal optimisation at least, it is also partly a function of design: some firms for example create elaborate chains of affiliates, holding companies and special purpose entities, designed to minimise taxes, but the consequence is also to obfuscate. Another factor that complicates the measurement of MNEs is the limited possibility for National Statistical Institutes (NSIs) to obtain a holistic view of their activities, reflecting legislation that typically restricts data collections to activities within their economy or (and only very rarely) to the global activities of firms headquartered in the economy (and even in these cases it is not clear that the coverage of the MNE’s activities is exhaustive). The sharing of data across countries could provide a window to provide this holistic view but legal constraints aimed at preserving confidentiality and privacy of respondents within national borders in most countries mean that this is not, at least for now, possible. To begin to address these challenges, the OECD has begun to develop an Analytical Database of Individual MNEs and their Affiliates (ADIMA), by compiling publicly available statistics on the scale and scope of the international activities of MNEs, thus providing a unique ‘whole of the MNE’ view.